1. Field of the Invention
The present invention relates to mass spectrometers, and in particular relates to a time-of-flight mass analyzer with a reflector having improved performance and to a method of operating a mass spectrometer.
2. Description of the Background
Mass spectrometry (MS) has long been used to provide both quantitative and qualitative data not easily available from other analytical techniques. The broad scope of MS technology has been used to provide molecular weight, empirical formula, isotope ratios, identification of functional groups, and elucidation of structure. A great deal of research has been expended in further developing mass spectrometry technology, and improvements in this technology offer realistic expectations of substantially increased use of this analytical procedure.
Since at least the mid 1970's, it has been known to use a mass reflectron in conjunction with mass spectrometry in order to improve performance. A mass reflectron for a time-of-flight mass spectrometer is disclosed in an article entitled "The Mass Reflectron, A New Nonmagnetic Time-of-Flight Mass Spectrometer with High Resolution" by Mamyrin et al. A mass spectrometer with an improved reflectron is discussed in an article by Gohl et al entitled "Time-of-Flight Mass Spectrometry for Ions of Large Energy Spread", with this latter reflectron utilizing a "two-stage mirror" to minimize ion flight time variations. A recent article entitled "A Secondary Ion Time-of-Flight Mass Spectrometer With an Ion Mirror" by Tang et al illustrated that the two-stage mirror concept does not provide substantially improved results over a single-stage mirror. Accordingly, much of the effort to improving mass spectrometry techniques has been directed away from improvements to the reflectron.
U.S. Pat. No. 4,778,993 is directed to time-of-flight (TOF) mass spectrometer which substantially eliminates interference with the analysis by ions of mass greater than the highest mass of interest. U.S. Pat. No. 4,883,958 discloses an interface for coupling liquid chromatography to solid or gas phase detectors. An improved technique for TOF mass analysis involving laser desorption is disclosed in U.S. Pat. No. 5,045,694. Matrix-assisted laser desorption mass spectrometry and a two-stage reflectron were discussed in an article in Rapid Communication in Mass Spectrometry, Vol. 5, pp 198-202 (1991). Additional background information regarding time-of-flight mass spectrometry is in a keynote lecture by LeBeyec published in Advances in Mass Spectrometry, Vol. II A, pp 126-145.
Further improvements in the performance of time-of-flight mass spectrometers are required for this analytical procedure to gain greater acceptance and become a standard analytical tool for increased uses. The disadvantages of the prior art are overcome by the present invention, and an improved time-of-flight mass analyzer and method are hereinafter disclosed for improving mass spectrometry performance. The present invention has a wide range of applications, and may be used with various methods of generating ions of interest.